In related art, an electrophotographic image forming apparatus has variations in mechanism dimensions or electrical characteristics of an image forming unit or the like. For this reason, even if an image with a uniform density is printed, there is a case where an image with a uniform print density may not be obtained due to the variations. Specifically, the variations in mechanism dimensions of the image forming unit or the like cause a density difference from the front to the rear in a main scanning direction.
In order to avoid the occurrence of a density difference, a method of using a correction table may be used. In the case of using the correction table, the image forming apparatus creates a correction table based on the reading result of a formed test image. Further, a service person or the like may adjust the created correction table. In this case, it may be difficult for the service person to appropriately determine the difference in density in the test image.